Air Conditioning and gas mileage?

[Docthrock]

My sales rep told me that the AC on the smart is not directly driven by the engine, but instead has an electric motor to drive the pump and blower. He also stated that running with the AC on is not going to change the gas mileage of my smart one iota.

When I turn the AC on, I hear/feel something dragging down. Is that the "massive" 90 amp alternator working overtime to run the AC? Seems like something starts dragging the car/engine down a little when the AC kicks on.

[SeaDoc]

scan guage shows a 5-7 mpg decrease when I turn on the AC... very consistent... anyone else looked into this?

[dcrooks]

So far, I have not noticed any difference with my gas mileage. It has been consistent with 39 MPG and I have had the A/C on a few times. Someone in AZ would know better...

[GHammerly]

Originally Posted by Docthrock

My sales rep told me that the AC on the smart is not directly driven by the engine, but instead has an electric motor to drive the pump and blower.

Wow! Who teaches these salesman all this BS...
Looks like a multi-rib drive belt driving the A/C pump, just like any other car.

[BimmerDob]

Running the A/C or even the headlights takes energy. If it had no effect on the gas milage, then that would be a bad design as you would then be paying the penalty when they are off for the extra load / drag / friction being put on the engine needlessly.

High School Physics: 3 laws of thermodynamics (paraphrased): you can't get something for nothing, you can't win, and you have to lose. Seems to also apply to car sales

[tivoboy]

I really don't think running the lights is going to impact MPG. The AC compressor is going to tax the engine directly though, and therefore WOULD impact MPG. The Alternator is going to be running regardless, and I don't think the draw from the lights is going to increase the impact of the already running alternator. I guess if all electrical systems drawing more than a few amps were OFF, no radio, nothing then the alternator might disengage and monitor battery power and charging. But, that doesn't seem too probable on this puppy

[Wizco]

Originally Posted by tivoboy

I really don't think running the lights is going to impact MPG. The AC compressor is going to tax the engine directly though, and therefore WOULD impact MPG. The Alternator is going to be running regardless, and I don't think the draw from the lights is going to increase the impact of the already running alternator. I guess if all electrical systems drawing more than a few amps were OFF, no radio, nothing then the alternator might disengage and monitor battery power and charging. But, that doesn't seem too probable on this puppy

Running lights may not make a measurable difference in mileage. But I can tell you that my non smart car, on a dyno, gives up a couple of horsepower with the dashboard fan on vs being off. It costs something to run anything.


AC obviously uses more power than headlights. Headlights use more power than the dash fan.

Oh, and before all you hypermilers take this the next extreme, the .005 mpg you save by driving with the lights off at dusk, will be more than offset by the insurance deductable for the fender bender you have when the other guy can't see you.;)

[tivoboy]

Sure, but I mean if the fan is ON already (or any other AC load device) the alternator is going to be running. I don't think putting on an additional current draw at that time is going to increase the load of the alternator, is it?

[gbryers]

Originally Posted by tivoboy

Sure, but I mean if the fan is ON already (or any other AC load device) the alternator is going to be running. I don't think putting on an additional current draw at that time is going to increase the load of the alternator, is it?

From a technical standpoint, all items using electricity, no matter how small, will have an impact on how hard the engine has to work, thus impacting mpg. However, a well-designed engine/electrical system takes much of the normal drag into account, and you won't see any really measurable reduction in your mileage. Large draws, such as A/C, however, are not "normal", and will reduce your mileage noticably.
If you are one of those people that insist that you don't have a stereo worth talking about until you can hear it in the next county, that, too, will reduce performance, but you may make up for it in prize money (BTW - check the sponsors are those events - if they are sponsored by the makers of hearing aids, you'll know what's up).
But that kind of thing aside, don't run around without headlights, neglecting to use turn signals, not running windshield wipers, etc., thinking you will save money. As previously noted, the cost of the tickets and accidents will more than off-set any savings.
There was also a study out in the 70's, when the first gas crunch hit (different story, same impact to the consumer), that running your A/C was more cost-effective than opening your windows. I have checked that in several of my vehicles, and I can attest that that may be true on large cars with lots of windows, but not all cars.

Cheers!

[Smartfor2guy]

Originally Posted by Docthrock

My sales rep told me that the AC on the smart is not directly driven by the engine, but instead has an electric motor to drive the pump and blower. He also stated that running with the AC on is not going to change the gas mileage of my smart one iota.

When I turn the AC on, I hear/feel something dragging down. Is that the "massive" 90 amp alternator working overtime to run the AC? Seems like something starts dragging the car/engine down a little when the AC kicks on.

Another misinformed uneducated or possibly smokin' crack salesman. The compressor runs off the engine drive belt like almost every other c`ar does. I have noticed it effects my gas mileage at least 2-4 mpg when in use